Production of all skin rayon



United States Patent 2,908,582 PRODUCTION OF ALL SKIN RAYON Marion R.Lytton, West Chester, Pa., assignor to American Viscose Corporation,Philadelphia, Pa., a corporation of Delaware No Drawing. Originalapplication June 29, 1955, Serial No. 518,987, now Patent No. 2,841,462,dated'July 1, 1958. Divided and this application July 2, 1957, SerialNo. 669,417

Claims. (Cl. 106-465) This invention relates to the production of shapedbodies of regenerated cellulose from viscose and more particularly tofilaments and fibers of regenerated cellulose from viscose.

' Y'In the conventional methods of producing shaped bodies ofregenerated cellulose from viscose, a suitable cellulosic material suchas purified cotton linters, wood pulp, mixtures thereof, and the like isfirst converted to an alkali cellulose by treatment with a caustic sodaso- Iution and after shredding the treated cellulose material, it isallowed to age. The aged alkali cellulose is then converted to aXanthate by treatment With carbon disulfide. The cellulose xanthate issubsequently dissolved in a caustic soda solution in an amountcalculated to provide a viscoseof the desired cellulose and alkalicontent. After filtration, the viscose solution is allowed to ripen andis subsequently extruded through a shaped orifice into a suitablecoagulating and regenerating bath. In the production of shaped bodiessuch as filaments, the viscose solution is extruded through a spinneretinto aycoagulating and regenerating bath consisting of an aqeous acidsolution containing zinc sulfate. The filament may subsequently bepassed through a hot aqueous bath Where it is stretched to improve itsproperties such as tensile strength. The filament may then be passedthrough a diluteaqueous solution of sulfuric acid and sodium sulfate tocomplete the regeneration of the cellulose, in case it is not completelyregenerated upon leaving the stretching stage. The filament issubsequently subjected to washing, purification, bleaching, possiblyothertreating operations and drying, being collected either before orafter these treatments.

. Thefilaments as formed by the conventional methods, consist of a skinor outer shell portion and a core portion with a sharp line ofdemarkation between the two. The cross-section of the filaments exhibitsa very irregular or crenulated exterior surface when even small amountsof zinc salts or certain other polyvalent metal salts are present in thespinning bath. The skin and core portions of the filament representdifferences in structure and these different portions possess differentswelling and staining characteristics, the latter permitting a readyidentification of skin and core. The sharply irregular and crenulatedsurface structure has a relatively low abrasion resistance and readilypicks up foreign particles such as dirt. Although the core portionpossesses a relatively high tensile strength, it has a lowabrasionresistance and a low flex-life, is subjected to fibrillationa'ndis relatively stiff. v It has now been discovered that the presence ofsmall amounts of alkali-soluble alkylene oxide adducts of p,p'- diphenolin viscose results in the production of shaped bodies of regeneratedcellulose such as filaments, films, sheets, and the like composed of allskin and having improved properties and characteristics providing thattheamount of the adduct is maintained Within certain limits and thecomposition of the spinning bath is maintained within certaincomposition limits which will be defined hereinafter. characteristics ascompared to conventional filaments The most readily distinguishableinclude a smooth, non-crenulated surface and the filaments consistentirely of skin.

This invention contemplates the use of such compounds as are moretechnically classed as polyoxyalkylene glycol ethers of p,p'-diphenolsuch as, for example, the ethers of ethylene and propylene glycols andp,p'-diphenol. It is obvious that for all practical purposes consideringcost, ease of preparation, commercial availability and solubility inwater and alkali solutions such as a 6% caustic solution, thepolyoxyethylene glycol ethers or ethylene oxide adducts of p,p-diphenolare preferred. Accordingly, the invention 'will be illustratedspecifically by reference to the polyoxyethylene glycol ethers ofphenol.

The polyoxyethylene content of the adducts or ethers may vary from about2 to 50 and more ethylene oxide units per molecule of p,p'-diphenol, thepreferred ethers containing from about 6 to about ethylene oxide unitsper molecule. The ether may be conveniently added to the viscose in theform of a solution in alkali or in Water. The. amount of the ether oradduct which is incorporated in the viscose must be at least about 0.5%by weight of the cellulose and may vary up to about 4%, preferably, theamount varies from about 1% to 2%. Lesser amounts do not result in theproduction of products consisting entirely of skin and greater amountsaffect adversely the physicalproperties of the products. Amounts Withinthe preferred range are most effective in enhancing the characteristicsand properties of the products. The ether or adduct may be added at anydesired stage in the production of the viscose, preferably being addedafter the cellulose xanthate has been dissolved in the caustic solution.

The viscose may contain from about 4% to about 8% cellulose, theparticular source of the cellulose being selected for the ultimate useof the regenerated cellulose product. Thercaustic soda content may befrom about 4% to about 8% and the carbon disulfide content may be fromabout 30% to about 50% based upon the Weight of the cellulose. Themodified viscose, that is, a viscose containing the small amount of theether or adduct, may have a salt test above about 7 and preferably aboveabout 9 at the time of spinning or extrusion.

In order to obtain the improvements enumerated hereinbefore, it isessential that the composition of the spinning bath be maintained Withina well defined range. The presence of the alkylene oxide adducts of p,diphenol in the viscose combined with these limited spinning bathsresults in the production of yarns of improved properties such as highabrasion resistance, high fatigue resistance and consisting of filamentscomposed entirely of skin.

Generically and in terms of the industrial art, the spinning bath is alow acid-high zinc spinning bath. The bath should contain from about 10%to about 25% sodium sulfate and from about 3% to about 15% zinc sulfate,preferably from 15% to 22% sodium sulfate and from 4% to 9% zincsulfate. Other metal sulfates such as iron, manganese, nickel andthelike may be present and may replace some of the zinc sulfate. Thetemperature of the spinning bath may vary from about 25 C. to about C.,preferably between about 45 C. to about 70 C. As is well known in theconventional practice in the art, certain of the physical propertiessuch as tensile strength vary directly with the temperature of thespinning bath. Thus, in the production of filaments for tire cordpurposes in accordance with the method of this invention, the spinningbath is preferably maintained at a temperature between about 55 C. and65 C. so as to obtain the desired high tensile strength.

The acid content of the spinning bath is balanced,

' against the composition of the viscose. The lower limit Patented Oct.13, 1 9

of the acid concentration, as is well known in the art, is just abovethe slubbing point, that is, the concentration at which small slubs ofuncoagulated viscose appear in the strand as it leaves the spinningbath. For commercial operations, the acid concentration is generallymaintained about 0.4% to 0.5% above'the slubbing point. For any specificviscose composition, the acid concentration of the spinning bath must bemaintained above the slubbing point and below the concentration at whichthe neutralization of the caustic of the viscose is sufficiently rapidto form a filament having a skin and core.

There is a maximum acid concentration for any specific viscosecomposition beyond which the neutralization is sufficiently rapid toproduce filaments having a skin and core. For example, in general, theacid concentration of the spinning baths which are satisfactory for thecommerical production of the all skin products from a 7% cellulose, 6%caustic viscose containing the ethers of p,p'-diphenol lies betweenabout 6% and about 8.5%. The acid concentration may be increased as theamount of additive is increased and also as the salt test of the viscoseis increased. There is an upper limit, however, for the acidconcentration based upon the amount of modifier and the concentration ofcaustic in the viscose. All skin products cannot be obtained if the acidcontent of the bath is increased above the maximum value al though theamount of added ether or modifier is increased beyond about 4% whileother conditions are maintained constant. For example, a viscosecontaining about 7.5% cellulose, about 6.5% caustic soda, about 41%carbon disulfide and 1% of a polyoxyethylene glycol ether ofp,p-diphenol containing about 20 ethylene oxide units per molecule andhaving a salt test of 9 to when ex truded into spinning baths containing16 to 20% sodium sulfate, 4 to 8% zinc sulfate and sulfuric acid notmore than about 8.6%, results in the production of all skin filaments.Lesser amounts of sulfuric acid may be employed. Greater amounts of acidresult in the production of products having skin and core. It has beendetermined that the maximum permissible acid content of the bath isapproximately 1.36 times the caustic soda content of the viscose and ispreferably maintained between about 1.2 and 1.3 times the caustic sodacontent of the viscose. A lowering of the amount of additive, thelowering of the caustic soda content or the lowering of the salt test ofthe viscose reduces the maximum permissible acid concentration for theproduction of all skin filaments.

The presence of the adducts or ethers in the viscose retards thecoagulation and, therefore, the amount of ether employed must be reducedat high spinning speeds. Thus, for optimum physical characteristics ofan all skin yarn formed from a viscose as above and at a spinning speedof about 50 meters per minute, the adduct is employed in amounts withinthe lower portion of the range, for example, about 1%. The determinationof the specific maximum and optimum concentration of acid for anyspecific viscose, spinning bath and spinning speed is a matter of simpleexperimentation for those skilled in the art. The extruded viscose must,of course, be immersed or maintained in the spinning bath for a periodsufficient to effect relatively complete coagulation of the viscose,that is, the coagulation must be sufiicient so that the filaments willnot adhere to each other as they are brought together and withdrawn fromthe bath.

In the production of filaments for such purposes as the fabrication oftire cord, the filaments are preferably stretched after removal from theinitial coagulation and regenerating bath. From the initial spinningbath, the filaments may be passed through a hot aqueous bath which mayconsist of hot water or a dilute acid solution and may be stretched fromabout 70% to about 110%, preferably between 80% and 100%. Yarns forother textile purposes may be stretched as low as 20%. The precise.amount of stretching will be dependent upon the desired tenacity andother properties and the specific type of product being produced. It isto be understood that the invention is not restricted to the productionof filaments and yarns but it is also applicable to other shaped bodiessuch as sheets, films, tubes and the like. The filaments may then bepassed through a final regenerating bath which may contain from about 1%to about 5% sulfuric acid and from about 1% to about 5% sodium sulfatewith or without small amounts of zinc sulfate if regeneration has notpreviously been completed.

The treatment following the final regenerating bath, orthe stretchingoperation where regeneration has been completed, may consist of awashing step, a desulfurizing step, the application of a finishing orplasticizing material and drying before or after collecting, or mayinclude other desired and conventional steps such as bleaching and thelike. The treatment after regeneration will be dictated by the specifictype of shaped body and the proposed use thereof.

Regenerated cellulose filaments prepared from. viscose containing thesmall amounts of the alkali-soluble alkylene oxide adducts ofp,p'-dipheno1 or the polyoxyalkylene glycol ethers of p,p'-diphenol andspun in the spinning baths of limited acid content have a smooth ornoncrenulated surface and consist substantially entirely of skin.Because of the uniformity of structure throughout the filament, theswelling and staining characteristics are uniform throughout thecross-section of the filament. Filaments produced pursuant to thisinvention and consisting entirely of skin have a high toughness and agreater flexing life which may be attributed by the uniformity in skinstructure through the filament. Although the twisting of conventionalfilaments, as in the production of tire cord, results in an appreciableloss of tensile strength, there is appreciably less loss in tensilestrength in the production of twisted cords from the filamentsconsisting entirely of skin. Filaments prepared from viscose containingthe alkylene oxide adducts of p,p'-diphenol have high abrasion andfatigue resistance characteristics and a high flex-life as compared tonormal regenerated cellulose. Such filaments are highly satisfactory forthe production of cords for the reinforcement of rubber products such aspneumatic tire casings, but the filaments are not restricted to suchuses and may be used for other textile applications.

The invention may be illustrated by reference to the preparation ofregenerated cellulose filaments from a viscose containing about 7.4%cellulose, about 6.6% caustic soda, and having a total carbon disulfidecontent of about 36% based on the weight of the cellulose. The viscosesolutions were prepared by xanthating alkali cellulose by theintroduction of 36% carbon disulfide, based on the weight of thecellulose, and churning for about 2 /2 hours. The cellulose xanthate wasthen dissolved in caustic soda solution. The polyoxyethylene glycolether of p,p'-diphenol was added to the caustic soda solution and mixedfor about /2 hour. The viscose was then allowed to ripen for about 30hours at 18 C.

Example 1 Approximately 1% of the polyoxyethylene glycol ether ofp,p'-diphenol, containing about 20 ethylene oxide units per molecule ofp,p-diphenol, was added to and incorporated in the viscose as describedabove. The viscose employed in the spinning of filaments had a salt testof 9.9. The viscose was extruded through a spinneret to form a 200denier, 100 filament yarn at a rate of about 22 meters per minute. Thecoagulating and regenerating bath was maintained at a temperature ofabout 60 C. and contained 8.1% sulfuric acid, 5% zinc sulfate and 16%sodium sulfate. The yarn was passed over a godet from which it wasconducted through a hot water bath maintained at about C. During thetravel through the hot water bath, the yarn was stretched approximatelyad m washed free of acid and salts and dried.

The individual filaments formed from viscose containifrig 1 the, etherof phenol have a smooth, non-crenulated exterior surface 'andconsistentirely of skin, no core being detectable'at high magnification '(e.g.'1500 The filaments of the control yarn exhibit a very irregular andserrated surface and are composed of about 55% skin and the balance corewith a sharp line of demarkation between the skin and core. Otherphysical properties are set forth in the table which follows Example 3.

Example 2 Approximately 1% of a polyoxyethylene glycol ether ofp,p'-diphenol, containing about 20 ethylene oxide units per molecule ofphenol, was added to and incorporated in the viscose as described above.The viscose had a salt test of 9.9 and was spun into a 200 denier, 100filament yarn by extrusion into a bath containing 8.5% sulfuric acid,zinc sulfate and 16% sodium sulfate. The bath was maintained at atemperature of 60 C. The extrusion rate was about 43 meters per minute.The yarn was passed over a godet from which it was conducted through ahot water bath maintained at about 95 C. During the travel through thehot water bath the yarn was stretched about 74%. The yarn was thencollected in a spinning box, washed free of acid and salts and dried.

The individual filaments were readily distinguishable from controlfilaments prepared from viscose containing no modifier in that they havea smooth, non-crenulated surface and consist entirely of skin. Controlfilaments have a very irregular and serrated surface and consist ofabout 55% skin and the balance core with a sharp line of demarkationbetween the skin and core. Other physical properties are set forth inthe table which follows Example 3.

Example 3 A control yarn was formed from a viscose as described abovewithout first adding an adduct of p,p'-diphenol. The viscose employed inthe spinning of filaments had a salt test of 9.7 and was extrudedthrough a spinneret to form a 200 denier, 120 filament yarn at a rate ofabout 22 meters per minute. The coagulating and regenerating bath wasmaintained at a temperature of about 60 C. and contained 8.1% sulfuricacid, 5% zinc sulfate and 16% sodium sulfate. The yarn was passed over agodet from which it was conducted through a hot water bath maintained atabout 95 C. During the travel through the hot water bath, the yarn wasstretched approximately 82% The yarn was then collected in a spinningbox, washed free of acid andsalts and dried.

The individual filaments formed from viscose containing no ether ofp,p'-diphenol exhibit a very irregular and serrated surface and arecomposed of about 55% skin and the balance core with a sharp line ofdemarkation between the skin and core. Other physical properties areincluded in the table which follows.

The improvements in the physical properties of viscose rayon and othershaped products obtained by the incorporation of the polyoxyethyleneglycol ethers of p, diphenol in the viscose are apparent from the tablewhich follows, the data being also representative of the generalimprovements for other polyoxyalkylene glycol ethers of g,p' diphenolcontaining different amounts of ethylene 0X1 e:

Although the tenacity and elongation are theonl'y properties set forth,they have been chosenbecauseof the easeand simplicity with which suchproperties may be determined. Insome instances, products made inaccordance with-this invention do not exhibit improve ments in tenacityand elongation, however, they consist of a smooth-surfaced, all skinstructure and possess improved abrasion resistance, flex-li-fe and otherproperties as disclosed hereinbefore.

One of the properties of viscose rayon which has limited its uses is itsrelatively high cross-sectional swelling when wet with water, thisswelling amounting to from about 65% to about for rayon produced byconventional methods. Rayon filaments produced in accordance with themethod of this invention have an appreciably lower cross-sectionalswelling characteristic, the swelling amounting to from about 45% toabout 60%.

The ethers of p,p-diphenol may be added to any desired viscose such asthose normally used in industry, the specific viscose composition setforth above, being merely for illustrative purposes. The adducts orethers may be added at any desired stage in the production of theviscose and may be present in the cellulosic raw material although itmay be necessary to adjust the amount present to produce a viscosehaving the proper proportion of the additive at the time of spinning.

The term skin is employed to designate that portion of regeneratedcellulose filaments which is permanently stained or dyed by thefollowing procedure: A microtome section of one or more of the filamentsmounted in a wax block is taken and mounted on a slide with Meyersalbumin fixative. After dewaxing in xylene, the section is placed insuccessive baths of 60% and 30% alcohol for a few moments each, and itis then stained in 2% aqueous solution of Victoria Blue BS conc.(General Dyestufis Corp.) for 1 to 2 hours. At this point, the entiresection is blue. By rinsing the section first in distilled water andthen in one or more baths composed of 10% water and dioxane for a periodvarying from 5 to 30 minutes depending on the particular filament, thedye is entirely removed from the core, leaving it restricted to the skinareas.

This application is a division of my copending application Serial No.518,987, filed June 29, 1955, now Patent No. 2,841,462, dated July 1,1958.

While preferred embodiments of the invention have been disclosed, thedescription is intended to be illustrative and it is to be understoodthat changes and variations may be made without departing from thespirit and scope of the invention as defined by the appended claims.

I claim:

1. A viscose spinning solution containing from about 0.5% to about 4%,based on the weight of the cellulose in the viscose, of analkali-soluble polyoxyalkylene glycol ether of p,p'-diphenol containingfrom about 2 to about 50 alkylene oxide units per molecule ofp,p'-diphenol.

2. A viscose spinning solution as defined in claim 1 wherein the etheris a polyoxyethylene glycol ether of p,p'-diphenol.

3. A viscose spinning solution containing from about 1% to about 2%,based on the weight of the cellulose in the viscose, of analkali-soluble polyoxyalkylene glycol ether of p,p-diphenol containingfrom about 6 to about 30 alkylene oxide units per molecule ofp,p'-diphcnol.

4. A viscose spinning solution as defined in claim 3 wherein the etheris a polyoxyethylene glycol ether of p,p'-diphenol.

5. A viscose spinning solution containing a small amount of analkali-soluble polyoxyalkylene glycol ether of p,p'-diphenol containingfrom about 2 to about 50 alkylene oxide units per molecule ofp,p'-diphenol, said small amount of the ether being a quantitysuflicient to impart a smooth, non-crenulated surface and asubstantially all skin structure to products formed by spinning theviscose at a sodium chloride salt test of at least 7 percentage ofcaustic soda in the viscose, but the quantity being insufficient toadversely affect the. physical properties of such products.

References Cited inthe file of this patent UNITED STATES PATENTS" PolakJuly 26, 1938 Collins Aug. 15', 1950 Cox Dec. 26, 1950.

1. A VISCOSE SPINNING SOLUTION CONTAINING FROM ABOUT 0.5% TO ABOUT 4%,BASED ON THE WEIGHT OF THE CELLULOSE IN THE VISCOSE, OF ANALKALI-SOLUBLE POLYOXYALKYLENE GLYCOL ETHER OF P,P''-DIPHENOL CONTAININGFROM ABOUT 2 TO ABOUT 50 ALKYLENE OXIDE UNITS PER MOLECULE OFP,P''-DIPHENOL.